1. Field of the Invention
This invention relates to improvements in cable spooling braking systems and more particularly, but not by way of limitation, to an improved back-up system for automatically locking an equalizer beam in a two-brake band drum braking system during failure of one of the brake bands.
2. Description of the Prior Art
The drawbacks utilized at the well site during the drilling of an oil and/or gas well bore normally induces a cable spooling drum having a relatively great length of cable or wire line spooled thereon for use during the drilling operation. These cable spooling drums are usually of a substantially large size in order to receive these great length of cable thereon, and comprise a cable receiving core having circumferential flanges provided at each end thereof for facilitating the spooling and unspooling of the cable and retaining the cable in position on the core. The outer periphery of each drum flange is normally provided with a braking surface, and an independent brake band is usually disposed around the drum flange for engagement with the braking surface to control the speed of rotation of the drum during a cable spooling or unspooling operation. In order to synchronize the operation of the two brake bands, or maintain a substantially equal braking pressure on each of the drum flanges, an equalizer beam is usually operably connected between the brake bands. The equalizer beam is pivotally mounted at a central point along the length thereof, and has the opposite ends secured independently to one end of the brake bands whereby the braking pressure applied to the end of each brake band is substantially equal at all times.
This equalizer beam arrangement frequently results in a send of false security at the drilling site since it is often mistakenly considered that the beam will maintain braking control of the spooling drum upon the failure of one of the brake bands. However, an extremely high leverage ratio is required to enable the brake band (mechanical brake) system to stop and hold enormous loads, and the loss of one band for any reason results in the loss of the mechanical braking system since the linkage cannot accommodate the extra level. Of course, it is the usual practice to provide an auxiliary brake system, but in actual working conditions, it is found that the normal auxiliary brakes will not stop the drill pipe moving downwardly in the well bore, but will merely slow it down. If the main brakes of the drawworks braking system fail, no presently available auxiliary braking system can provide a final stopping of the drill pipe